Piezoelectric devices are well known in the art and include crystal oscillators and surface acoustic wave resonators. A piezoelectric device may be considered any material that demonstrates piezoelectric behavior.
Most of these devices comprise a thin slab of quartz upon which are deposited thin metallic electrodes. The electrical characteristics of these devices depend upon many factors including the quartz's temperature, the orientation of how the quartz slab is cut, the physical dimensions of the slab, as well as the number and dimensions of electrodes deposited on the surface of the quartz.
In virtually all piezoelectric devices, once the dimension and the geometry of the quartz slab are selected, the sole remaining variable that affects a piezoelectric devices performance are the number and dimensions of the electrodes. For example, it is well known that a quartz resonator, comprising a particular slab of quartz and at least two electrodes on opposing faces of the quartz, will have its resonant frequency determined, in part, by the size and thickness of the electrodes deposited on it. Moreover, for an electrode of any given area, the resonant frequency of a quartz resonator can be lowered by increasing the thickness, (i.e. mass loading) of the electrode while the resonant frequency can be increased by decreasing the thickness or mass of the electrode. A monolithic quartz filter which generally comprises two or more individual resonator stages on a single piece of quartz, has its characteristics, including pass-band frequency and bandwidth and input-output coupling, determined in large part not only by the geometry of the crystal cut but the thickness and surface area of the electrodes as well.
In the manufacture of piezoelectric devices, after the quartz geometry is selected, the electrodes are deposited onto the surface of the quartz using well known techniques such as sputtering, vapor deposition, and so forth. Final tuning of a quartz or piezoelectric device typically involves either selective removal of electrode material (which is exceedingly tedious) or it may include an addition to conductive electrode material in a controlled environment to bring the device to a desired set of specifications.
A major source of defects in the manufacture of packaged piezoelectric devices, (i.e. metallized quartz slabs) mounted in a sealed or hermetically sealed container, is the frequency shift experienced when an otherwise tuned piezoelectric element is mounted in a hermetically sealed package. Even during the manufacture of electronic circuit boards using so-called surface mount piezoelectric packages, the metallized quartz crystals are positioned in a package or case which is evacuated, sealed with an appropriate material, heated at some temperature during the sealing process and during the assembly process of a circuit board and then cooled. During the final manufacturing of the crystal package itself wherein the metallized quartz is mounted in a package, as well as final assembly of an electronic circuit board, the desired operating frequency characteristics of piezoelectric devices invariably changes, even if only slightly, from that which was obtained during the final tuning of the piezoelectric but element before its insertion into the package, and in many instances rendering an unusable, defective part.
Prior art solutions for this frequency shift experienced during the manufacture of packaged piezoelectric devices, has been a compensation for an expected frequency shift encountered during the packaging of the devices. For example, if a quartz resonator is desired to have a resonant frequency of 45.00 MHz but it is known that through the packaging process of the quartz slab its resonant frequency decreases by 2000 Hz, the resonant frequency at the finish plate operation in the quartz final tuning process can be adjusted to be 45 MHz plus the 2000 Hz lost during the packaging process. This prior art technique, however, relies upon an otherwise imperfect manufacturing process to continuously insert the same defect, i.e. the same frequency shift, to the finished pieces.
An improved package for electronic components, such as piezoelectric devices that require precise addition or subtraction of material to their surfaces to accomplish or to effect their final operating characteristics, and one that avoids having to rely upon added defect consistency, would be an improvement over the prior art. Such a package might even allow for frequency adjustments to be made even if the device is installed in a circuit board.